The NSManagedObjectContext manages all the data stored in the persistent store and is responsible for the reading and writing of data to and from that store. Normally, an application will initialize the context as part of its startup routines and then do a save during shutdown.
For a context to be used, it needs to be attached to a NSPersistentStoreCoordinator. The coordinator represents the actual data stored on the disk. For most normal applications, it is unnecessary to deal with the coordinator directly, except to initialize the context.